Oxford University researchers have concluded that the more intelligent a person is the more likely they are to trust other people. This is assumed to be the case because smarter people have a better at determining what sort of people they want to be around and self-select to be around people who can indeed be trusted. The study also points out the benefits of trust for society at large (including not intelligent people).
The Oxford researchers found, however, that the links between trust and health, and between trust and happiness, are not explained by intelligence. For example, individuals who trust others might have only reported better health and greater happiness because they were more intelligent. But this turns out not to be the case. The finding confirms that trust is a valuable resource for an individual, and is not simply a proxy for intelligence.